Quenching effects of (-)-Epigallocatechin gallate for singlet oxygen production and its protection against oxidative damage induced by Ce6-mediated photodynamic therapy in vitro.

BACKGROUND

Singlet oxygen (O) is highly reactive to biological components such as lipids, proteins and DNA, which induces oxidative damage to cells and tissues. Natural antioxidants may function as O quencher to prevent O involved photosensitized oxidation in biological system.

METHODS

Time-resolved measurement of O luminescence was employed to evaluate the O quenching abilities of natural antioxidants in air-statured phosphate buffered saline (PBS), including (-)-Epigallocatechin gallate (EGCG), Proanthocyanidins, L-carnosine and Vitamin C. The O quenching effects and rate constant of EGCG were investigated by detecting the absorption, fluorescence and H-NMR spectroscopy and O luminescence decay curves, respectively. In addition, the protective activity of EGCG against O oxidative damage caused by Ce6-mediated photodynamic therapy (PDT) was verified in cells.

RESULTS

EGCG, proanthocyanidins, L-carnosine and Vitamin C efficiently quenched O luminescence at 1270 nm. The triplet-state quenching rate constants of EGCG for Rose Bengal (RB), Chlorin e6, AlPcS and HiPorfin are 2.21 × 10, 4.90 × 10, 3.30 × 10, 1.78 × 10 Ms, while the O quenching rate constants are 2.80 × 10, 1.50 × 10, 1.30 × 10, 1.70 × 10 Ms, respectively. Furthermore, EGCG could effectively quench O production to prevent NIH/3T3 cells oxidative damage induced by Ce6-mediated PDT.

CONCLUSIONS

EGCG is an efficient quencher for both triplet-state photosensitizers and O. The quenching ability of EGCG during photosensitization for selected photosensitizers is: RB > HiPorfin > Ce6 > AlPcS. EGCG could be used to protect normal cells and tissue against oxidative damage.